Java runtime needed even if not using the JVM. Error message is not very helpful

[scuellar]

I'm running

% cabal run saw -w ghc-8.10   
Up to date
saw: user error (/usr/bin/java returned non-zero exit code: ExitFailure 1
Standard output:

Standard error:
The operation couldn’t be completed. Unable to locate a Java Runtime.
Please visit http://www.java.com for information on installing Java.


)

I'm not sure why I need java runtime. A better error message could be helpful.

[RyanGlScott]

Ouch, that is unfortunate. By default, if SAW cannot find a Java installation at startup, then it doesn't perform any additional work. But you are in a strange situation where you do have Java installed /usr/bin/java, but it returns an unexpected error code due to some sort of misconfiguration.

In any case, having SAW simply error out at startup when you're not using the JVM-related functionality is a pretty poor user experience. We should at least check to see if java returns non-zero exit code, and if so, convert the error above into a warning so that SAW can still proceed.

[scuellar]

In my case, all java was installed but not linked properly. For future reference use
brew info openjdk

Which informs you that you need to symlink it with

 sudo ln -sfn /usr/local/opt/openjdk/libexec/openjdk.jdk /Library/Java/JavaVirtualMachines/openjdk.jdk

That did the trick.

[sauclovian-g]

Given that this happens by default on macos, maybe we should add logic to try to check for that case and print something helpful.